Project-omicran-graph



April 28, 1953 L. vALols l 2,636,271

PROJECT-o-GRAPH l Filed May 5, 1951 v 4 Sheets-Sheet l gf f u d l 5 i l gf! B a 12 CI O/ 1(29 Q1 WIW/iIIINMIILQH/f gil-lim! Inventor' leb/z Valais' April 28, 1953 l.. vA| o|s v 2,636,271

PROJECT-O-GRAPH Filed May 5, 1951 4 Sheets-Sheet 2 InventorI Zeb/z d/alfs* attorneys April 28, 1953 vALols 2,636,271

PROJECT-o-GRAPH Filed May 5, 1951 4 Sheets-Sheet 3 Inventor1 e/z Valais April 28, 1953 L. vALols 2,636,271

PROJECT-O-GRAPH Filed May 5, v1951 4 Sheets-Sheet 4.

,//L (115mg jung! I 72 24 Inventr Patented Apr. 2%, 1953 UNITED STATE-.S @FFIQE PREEGT-O-GRRPH Hon valbisgrsillery, Quebiecgg.Canada.V

Application`lV1`ay5195LSeraPNz 224.7732

The present intention relateeftoa drafting in strument and more-particularly to admitting instrument of the planograph class which provides? mea-ns to retrace a drawng'n suoli.l a manner that' its dimensions' will be/changedin one` direc@ tion only.

The drafting instruments' according to'v the iir-FV vention maybe properlyvl called? a proieetoerapnf because tine1 drawing obtained' thereby censita tutes a projection of the originaildrawirig The instrument according'to' thefpresentl invention dinerent from a pantograplli.' in. the latter instrument a drawing may loe reduced? or` inereased in Size equal-Iy in` all directions: whereasfwitlithe projeetograpnraccord-ing tof-the invention the drawing isrediiceci-Y or increasedirr size in only one direction While-f iti-iel reproduced to its true dimensionsl in'y the direction at riglfitg. angles to the lrstone;

Drafting instruments oti the character de scribed have already been`V constmated:l inwhich am'4 is: s-lidablyV pivotedi atene end carries` a tracing and` ai marking stylus-:whereby a drawf ing may be recopied or retraced and at thesame'4 time have their dimensions varied tor'presenit a picture. with4 anv elongated? or: datori-ned* appear@ ance and; design.. Biotintlieseinasstrmroaentse.triei Styli move overamore oirlessreirculaar or averted-iev` patln,. therefore they" cannon` loe.` considere@ varying the dimensions of? the:drawingsctireetion oniriis the'.k caser. for the present iseapalalleiin highlwacfeuratermannentog retrace a drawing.. with: ridefinizione mi" diman-m eion's' in one. dimectiom onlyl vrhu'ez ther direction. at'. right.n to the' first: willi he retrace-d toi. theirI true:

Stili.. another. important: attent of; invention. is; a drafting instrument chair-.- aeter describe-rl. which ther ratio: ot reduction orvinorease.-

loe: continuously varied ai to ai, maxmiirnilimiti.

Still another-important objeot of tlsie invention is the provision: of ai. draitirxg;` instru nient of the character:l described im retraoinginayfbefeeeted witlnhigfh aecuraoyyloemcause the. inherent unc-:duels frieional .resistaneesr various directions-.oli movement of.l tiietylkare made: ineffective lay the addition ot. a` substanr" tiaily uniform inf-:tionalv resistance. of; a.. higher. order: this. is. doneloy; providingthe,in.-` strnmenttwthi a. sog-callediction; drownen inthe.. form.. of. a. plate.- adaptedl tof come. into, rictional; contact with the drafting table.

Still anotlrenirn. iolojeotothepreeenti invention'.- isz-the' provision .uit instrument the character described which is capable.-- ofl drawing ellipsesf of?. dirfterent. shapes. and. dimensione item1 acircie:amdgalsorparabelae oivarieuef shapes from; gieren-sparanoia.l

YetiA another: important: object. of the.V present invention iey previsioni' of, anA iraxstrtunen-t.V of ti-feelfiaracter dieserihediwhich Wil-'1 loertrundevery; convenienti' iin trie :drawing-got. isometre and l-ilee.. piotoria'fviewsfronr plane..eflevatiomal.naridorsecv tionaliviietvs odian. obect..

Yeti. another" irritiert:ant7 obgiecti of; the;- present invention: is; the.: provisoir o a drafting'.E instru-- mentf: of: the. characterv described I. which;` beV used; an.v mort-broden manner' to' do.- ramer'v lettering;

Tnefforegoing: aridi other; iimportant` oloiiects or. the presentiirventoniwlli beeomemore apparent... dining, the ,following disclosure referring. to the drawings in which:

Figures Lf is aperspe'ctiveivew ofl the; drafting instrument" to.y tries, invention in. Anee om ara-drafting tab1e;.

Eigurei 2. ier asA plan,` ot. tloe-z` same.. showing.; one.; application-of, the Yinstrument-;l f

Figurer 3:15am schematicsview 1',l'1e,r;\rin:` ciplessofifunetoningofi theiinstrument according toiftheefinventiorr; Eguree.4--.and. 5 thesuc eeseive;` steps for'. draw-ing ai. block daerarnfrom. theetraeine;V etteetedlcn(`l theinstrumenttaccordi'nge to'fthe-i inventiom.

Figure 6 shows in plan a modification ofithe; instrument according tothe invention;

Figure 'l-shows-another. applioathn of 'Y strumentzaccordingftothe invention for drawing.

ellipses trenta circle;i

Figmzedie a. sectionalongmline 8.4-8 ot' Figure '7;T

Eigure .9: shows. still another, application. ofthe'r invention in which parabolaeofdifferent shapesl nia-y;l loeL drawn,l from .a `given .parabo1'a;,

Irigures@ 1.0 and are. schematic views. of. parabol'ae retracted. wtfitheiidimensins recliioed respectively, along.A tleXand'; Y? axes Figure; LZLi'SiarbrOReIt sectonalleleivation ofthe. instrum'entaccond'ing topte. invention;

Eigure L4. is. a. crossf-sectional elevation along' Figure'z 15isl an, enlarge'dsectional elevation (ifr` the. sof called friction dro'vvner.'v according toi tiief invention;v and;

Figgar'e; lid; is anl elevationoffthe tracing stylirsf usted with v a. guidi'lrgzdsc shownV inv sectionxfortlre: applicatinillst'ate'd in Figure" 9.'

Referring now more particularly to the drawings in which like reference characters indicate like elements throughout, the instrument according to the present invention comprises a rigid triangular frame generally indicated by the letter A movable over the fiat surface of the drafting table B. The triangular frame A is adapted to move along a straight line without rotation over the table B.

In order to obtain this displacement, at the ends of the straight hollow base member I of the triangular frame A are mounted a pair of gear wheels 2 of equal diameter keyed to a common shaft 3 shown in Figure 12 which shaft extends through the entire length of the base member I.

y block 23 threadedly receiving a horizontally ex- The gear wheels 2 are adapted to come in meshing engagement with the straight parallel racks 4 rigidly mounted on the parallel legs of a rigid U-shaped frame 5 laid on the table B. Because the gear wheels 2 revolve exactly in unison, the triangular frame A will always move along a line perpendicular to the cross-member 5' of the frame 5. l

The gear wheels 2 have a flange 2 projecting from their inner peripheral edge to prevent sideways disengagement Tfrom the racks 4.

The .triangular frame A is supported at its apex by means of an idle wheel 'I freely rotatable over the table B in a plane parallel to the planes of rotation of the gear wheels 2; The wheel 'l is journalled in a-bracket l secured underneath the plate B secured to the apex of the frame A.

A straight bar 8 is removably supported on the triangular frame A and more particularly on the straight side members 9 of said triangular frame.

This bar 8 has preferably a square cross-section and is hollow to slidably receive a pair of blocks II) shown in Figure 12 provided with a downwardly extending pin II for removably engaging any one 'of a plurality of spaced holes I2 made on f both side members 9. l The holes I2 are opposed in pairs on each side member 9 such that the distance of the holes in each pair from the base member I is always equal. Thus when the pins II of the bar 8 are inserted into the holes I2 of any one of these pairs, the bar 8 will be parallel to the base member I The distance from the base member I of the successive holes I2 on any one of the side members 9 is conveniently chosen to obtain successive steps in the variation of reduction or increase ratios of the drawing instrument according to the invention.

Stylus carrying members I3 and I4 having an inverted U-shaped cross-section are slidably mounted on the base member I and the bar 8 respectively. As' shown in Figures 13 and 14. the members I3 and Ill are preferably mounted on roller lbearings 5I partially imbedded in the top portion of said members. y

y The styluscarryingmembers I3 and Ill may mount alternatively a marking or a tracing stylus. In the figures, the tracing` stylus I5 is shown secured to the carrying member I3 for displacement along the base member I of the triangular frame A While the marking stylus It is securedY tothe carrying member I4 and is displaceable along the bar 8.

A straight elongated arm I7 is pivoted at the.

apex portion of the triangular frame A and' is pivotally connected to the carrying member I3 by receiving a pin 'I8 projecting upwardly from said carrying member I3. The straight arm II' is also provided with a longitudinal groove I9 shown in Figure 12 extending asubstantial distance undertending bolt 2li which is rotatably journalled underneath the apex plate 6 of the frame A. A knurled knob 25 is secured to the projecting end of the bolt 24 for rotation of the same and displacement of the block 23 and pivot pin 22. The latter projects through a longitudinal slot 26 made in the apex plate t. To lock the pivot pin 22 in a given adjusted position the latter is threaded to receive a locking collar 2l the rotation of which will grip the plate Il between itself and the block 23. .l

The length of displacement of the pivot pin 22 relatively to the triangular frame A, will be such as to ensure a continuous variation in the increase or reduction ratio of the projectograph from a maximum to a minimum limit when adjusted in cooperation with the setting of the movable bar 8 in holes I2.

Therefore for obtaining a given ratio of increase or reduction, the movable bar 8 will be rst set in the pair of holes I2 which will give a value nearest to said desired ratio and a final adjustment will be effected through knob 25 by adjusting the position of the pivot pin 22 opposite the desired graduation of the scale 28 marked along an edge of the slot 2| of the arm I1. The scale 28 will give the distance from the pivot pin 22 to the base member I.

With this arrangement a continuous increase or decrease in the ratio of reduction or increase of the instrument is obtained with a very high accuracy.

The length of the longitudinal slot 2I of the arm I1 will be such as to take care of the longitudinal displacement of the pivot pin 22 and also the displacement of the arm I1 when the latter is pivoted on said pivot pin 22 from side to side of the triangular frame A.

The arm I'I preferably extends outwardly from the base member I of the triangular frame at its end opposite the slot 2| to form a manipulating projection 29 at the free end of which is removably secured the manipulating device generally indicated bythe letter C.

Said manipulating device comprises a disc 30 of relatively substantial diameter horizontally disposed and adapted to frictionally contact the surface of the drafting table B, said disc 30 lbeing rigidly secured to the upright shank 3| the upper end of which is bored to receive the tapered end of a rod 32 freely engaging a hole 33 made at the free end of the arm projection 29 said rod 32 being terminated at its upper l' end'by a stop' ian'ge 34. To remove the manipulating device C` from the arm II it is only necessary to disengage the tapered end of the rod 32 from the bored end of the shank 3|.

The drafting instrument according to the invention is normally operated as shown in Figure 5;. on instrument. haizeebeerrredneedftoz. ai muni; itfis necessary tn` add; airicticnalg; resists ance. on. 1cm-ich:y greater value: thans;y said: inherentv fractional resistances: ci; thev instrumenta which additional. resistance will; be equal in all direc ci; movement; Sucht an additional resistance; ist provided; by" the: disc. at.. oi the manipnlatingrdevicer Cf md latten'is propere lycaflled a frietionzdrovvnerz When the: instrument. is. used-.zwith'.4 a `template such. as. the template'.` shown; iml'eigure, 9 'the tracing, stylus is prederalfily provided with a permeated guidingf dise. 31T showin- Figure 1:6 madeoi transparent materiaiandengaging the free point 38 of said stylus I5 to abut; the

slfronlderiiiotftheisame and rest'oirthe edgelof trie;t'eiriplate35il in'isuchai mannerfto preventicons taut ofthe free point; isili with;` tlezsurfezce of the drafting table;v

, Figure 6'shows.'atmodincationc'of:the.straight arman.' which ispivoted onbut-.isnot slidablefrelatively. to tliepivotpin; zaand is pivotally and slid ably connected to. thezstyluszcarryingmember: I3` atthebasememben Il; the pin l8r oisaidy carrying membenengaging'the corresponding slot. 2l.'v ci With.: this modicatiom. the strains" caused-t by.

the: displacierrnent1ofI the proiect'ograph: will'f be carriediby thelpivonpirr 212' andnnorrby'the base member. I..

The i drafting instrument according' to the. inventionis used to advantage in the? preparation tif-isometric.' drawings, pictorial perspectives and bloclcldagramsg. an example of the latter being shown in Figures 2 to 5.. In this example, a e.; be proportional@ meamounrof" increase'iratic contour. map D' is'y laidtf on the; drawing table' B atariz angle relatively toftlfiedireetion of displacement of the projectograph preferably at` 4'5" angleiandsaid"contburmap isl retraced at E with a. reduction. oi allthe dimensions lying at'right angles to: the line of' displacement cf the tri angular frame A. There.isfobtainedA al parallelo@ gramwith all'. thecontour lines deformed accordingly. AsshowninFiguresl and 5a block diagram may be prepared directlyfrcm Said: re sintin'gA parallelo'gram..V For exa-mpie. the.' block 5t, shown in Figures4 is drawn en'tracingf-y paper withv contour line levels.. 521r marked along: one or more` corners of the-'block 5i. Lines 533'. 53! are thenldrawn parallel tothe base 5410i the bloei:` 5|, at each level 52. The parallel'cgrain.` E is the-nplaced'v under theftraeingfpaper so that' its edges will register with the' lines! 53` at level marrer 9?. and then thev contour line 91 of' the parallelcgram is retraced on the block@ 51` asl shown in Figure 41. The parallelogram. E is next displaced so that its edges register with theline- 53' at level marked mand the contour line mici theparallelogram- E is retraced on the block:l 5f.. This procedure is' continued. for: all the. contour' lines. until the final block' diagram 55,1. shown in Figuresis obtained,l

Referring" to Figure 3, it willl be: noted that alittle-dimensions ofthe original map D and map parallel te' therlongitudinal. axis XX of the projectograph are?. respectively equal, for instance the distance a is` equal to ai' onlyy the.; dimensions lying. at" right angles to` said axis XX arereduced. inthe retraced mapiE Also a it. should be noted that; the displacement b. of the stylus measured. along a liney parallel to.` the axis.l XX willl he equal to;v the'displacement li of the pivot ci the`r l'l along-` the' axis; Similarlyci'sequal to cfV andd issu-ual tod?.

Theinstrument according, to the. nventionimay 6 also used retracingzi eillpseef on any1 desiredicontom: from; a: circle.

As shown in Figure 7 a circular movement of the desired diameter may be imparted to the tracingstyl'us f5EV of' the instrument means ofZ an auxiliary device or circletracer'f generali. ly indicated by theletterilf.' devicesconr prisesl a straight scalefmeinber 4in on. is sl-idable asshownin;Figuret` eli-sleeve et' which may be clamped any-desireclpositionailon.

said scale member 40 by; a set screw 42. The sleeve 4I carriesfa'table. engaging pin 43 rigidly secured to the underface thereof. At the outer end of* the scalememberV M* is provided: a cup shaped recess or hole-"Mier receiving tinr-.p'oi'r'it of the tracing stylus-= t5; theI pin 413? the center of the circle and the scale member 40 the radius of the ...same It will be obvious that the tracing stylus engaging the cup shaped recess. or hole 44 will trace a circle the radius of the circle from which it is retraced'anditliie length of its short axis will depend on the reduction factor at which the projectograph is set. Qbviously if the marking. stylus L6 is placed at. the outer end'A ofV the" armi. t1 and the device: H

f z together'wtl tlie tracing stylus" 15T placedatithe trace' any parabola from a first parabola .ofjwlficli the parameter p is known. The rst' parabolawill be provided by the template 36 one edge 45 of which has a parabolic contour, and the tracing stylus l5 will be. provided witlithe.1 transparent guidi-ng disc'l to follolw.. said` parabolic` edgei. and thereby the. second paraboliccurve. 45;. will be retraced by the markingstylus. Hi..

The equation .of the parabola .4.11 shown in Figeure; 1.1 and havinga directriX-.-M is.

The new. paraboiaw Qbtainedty. modification. ofthe scale a, direction parallel' to. fe-YZ Therefore, te; a parabolaioii. panameter pff from.y an.: original parabola of: parameter?. n; the. adiustment of., thefamlaratus. is...cailculatedeas follows:

if the variation of the scale is paralleli' to` tliey of: the: parabola..

Similarly the new." parabola; -isobtained? hy; mndicatdort of;- the: ai direction: paralleli tothe X axis as shown in Figure 10, one can obtain a new curve 49 the equation of which is:

y2=2pl1xll in which :1W-:ra: and p"=new parameter, 1 being the factor of modification given by the adjustment of the projectograph.

The value of the new parameter in relation to the value o f the parameter of the initial parabola 5U may be calculated as follows:

Therefore, to obtain a parabola of parameter p" from an original parabola of parameter p the adjustment of the apparatus is calculated as follows:

'EPH if the variation of the scale is parallel to the axis of the parabola.

When the instrument is used for reducing, the factor 1- becomes a reduction factor and is given by the formula wherein L is the distance from the base member l to the pivot pin 22; m is the distance from the movable bar 8 to the pivot pin 22, and n is the distance between the movable bar 8 and the base member l (see Figure 9).

L may vary about 4 inches due to the longitudinal adjustment of the pivot pin 22 on the triangular frame A. To obtain a desired reduction, the movable bar 8 is iirst set into the desired pair of holes l2 and the final adjustment is made by setting the pivot pin 22, said setting being given by the formula:

Varying the height of the triangle with the adjustable pivot pin 22 assures a greater accuracy of the reduction factor because any displacement of the movable bar corresponds to a greater displacement of said pivot pin. Also the parallelism of the base member l and the movable bar 8 is not dependent on the operator.

While preferred embodiments according to the present invention have beenl illustrated and described, it is understood that various modifications may be resorted to Without departing from the spirit and scope. of the appended claims.

What I claim is:

1. VA'n instrument of the character described comprising a frame displaceable along a straight line and` without rotation, two straight spaced members mounted on said frame and extending transversely to the direction of displacement of the same, a pivot mounted on said frame at a predetermined distance from said members, a stylus carrying member slidably mounted on each of said members, a pivot mounted on each of said stylus carrying members, and anv arm pivoted on one of said three pivots and slidably and pivotally mounted on the other two pivots whereby arcuate movements of said arm about said first mentioned pivot will cause the displacement of said stylus carrying members along said transverse members.

2. An instrument of the character described comprising a movable frame, means for guiding thedsplacement of said framealong a straight line and without rotation, two straight spaced` members mounted on said frame andextending4 transversely to the direction of displacement of:

said'. frame, a pivot xedly mounted on said frame at a predetermined distance from said straight members, a straight arm pivoted on said pivot, a stylus carrying member slidably mounted on each one of said straight members and each having a pivot engaging said arm along a straight line? passing through said rst mentioned pivot, said arm being longitudinally slidable relatively to two of said pivots, whereby the arcuate movement of said arm will displace said stylus carryingz members along their respective straight members.

3. An instrument of the character described comprising a movable frame, means for guiding the displacement of said frame along a straight line and without rotation, two straight spaced members mounted on said frame and extending transversely to the direction of displacement of said frame, a pivot xedly mounted on said frame at a predetermined distance from said straight members, a straight arm slidably and pivotally mounted on said pivot, a stylus carrying member slidably mounted on one of said straight members and slidably and pivotally connected to said arm, another stylus carrying member slidably mounted on the other of said straight members and pivotally connected to said arm along a straight line passing through the pivot connection of said arm to said frame whereby the arcuate movement of said arm will displace said stylus carrying members along their respective straight members.

4. An instrument of the character described comprising a movable frame, means for guiding the displacement of said frame along a straight line and without rotation, two straight spaced members mounted on said frame and extending transversely to the direction of displacement of said frame, a straight arm pivotally mounted on said frame on a xed pivot spaced from said straight members, a stylus carrying member slidably mounted on each one of saidstraight members and slidably and pivotally Aconnected to said arm along a straight line passing through the pivot connection of said arm to said frame whereby the arcuate movement of said arm will displace said stylus carrying members along their respective straight members.

. 5. An instrument of the character described comprising a movable frame, means for guiding the displacement of said frame along a straight line without rotation, two straight spaced members mounted on said frame and extending transversely to the direction of displacement of said frame, a pivot mounted on said frame at a point spaced from said straight members, a straight arm pivoted on said pivot, a stylus carrying member slidably mounted on each of said straight members and connected to saidarm at the intersection of the latter with said straight members. at least one of said stylus carrying members being slidable relatively to said arm, a marking stylus and a tracing stylus carriedby said stylus carrying members.

6. A drafting instrument of the character described comprising a frame movable over a flat surface, means for guiding the displacement of said frame along a straight line and without rotation over said flat surface, two spaced straight members mounted on said frame and extending transversely to the direction of displacement of said frame, means to adjustably the distance separating fsaid straight-members, fai-pivot lmounted fon `said frame-fat fa point spaced from said straight members, an arm `pivotedionisaid lpivot, a stylus carrying member slidablyv mounted on each of said straight members and connected to arm to beidisplacedthereby along saidmemders.

7. A- drafting instrument of the character described comprising a frame movable overaflat surface, means for 41guiding the displacement of said frame along a straight line and Without rotation, two straight spaced members mounted on said frame and extending transversely to the direction of displacement of said frame, an arm pivoted on said frame at a point spaced from said straight members, a stylus carrying member slidably mounted on each of said members, one of said straight members rigidly fixed relatively to said frame and extending at right angles relatively to the direction of displacement of said frame, the stylus carrying member slidably mounted on said fixed member being pivotally connected to said arm, the other of said straight members being removably mounted on said frame and securable at predetermined varying distances from said fixed member, the stylus carrying member mounted on said removable member being pivotally connected to said arm, whereby the arcuate movement of said arm will displace said stylus carrying members along said straight members.

8. A drafting instrument of the character described, comprising a frame movable over a flat surface, means for guiding the displacement of said frame along a straight line and Without rotation over said fiat surface, said frame including an integral member extending transversely to the direction of displacement of said frame; a second member removably aiixable to said frame, means to secure said second member to said frame at various pre-determined distances from said first member, a pivot pin mounted on said frame at a point spaced from said two members, an arm engaging said pivot pin, a stylus carrying member slidably mounted on each of said members and connected to said arm to be displaced thereby along said members.

9. A drafting instrument of the character described, comprising a frame movable over a flat surface, means for guiding the displacement of said frame along a straight line and without rotation, an integral straight member of said frame lying transversely of the direction of displacement of said frame, a second straight member removably aiiixable to said frame at predetermined varying distances from said first integral member, a pivot pin mounted on said frame at a peint spaced from said two members, an arm pivctally engaging said pivot pin, a stylus carrying member slidably mounted on each of said straight members and connected to said arm at the inter-sections of the latter with said straight members whereby the arcuate movement of said arm displaces said stylus carrying members on said straight members, a tracing stylus and a marking stylus mounted on said stylus carrying members, the position of said Styli being interchangeable.

l0. A drafting instrument of the character described, comprising a frame movable over a flat surface, means for guiding the displacement of said frame along a straight line and Without rotation over said flat surface, said frame including a first integral straight member extending transversely to the direction of displacement of sai/d iframe, :a 'second straight' #member removably amable to said :iframe at `pre-fdstern-fined vvarying distances Vffrom said first .straight member, pivot pin `-mei-interi on sai-tl frame a't (a point spaced from said two straight members, Lsaid pivot adj'ustablydisplaceable on said fra-me for varying its distance from fsa'id nrst Istr-aight member, an arm having one end engaging :said pifvot'pinto pivot on-said 'frame,=said -ar-m proiecting --at its other end flfrom vsaid -first member, a Iplate `depending r`-morn vsaid fproectirrg :en/d. vd'of said arm adapted to come into frictional contact with said flat surface, a stylus carrying member slidably mounted on each of said straight members, a tracing stylus and a marking stylus respectively connected to said stylus carrying members, the stylus carrying member mounted on said first straight member being pivotally connected to said arm at the inter-section thereof with said rst member, the stylus carrying member slidably mounted on said second straight member being pivotally mounted on said arm at the inter-section of the latter with said second member.

1l. A drafting instrument of the character described, comprising a frame movable over a flat surface in combination With means for guiding the displacement of said frame along a straight line and Without rotation comprising a shaft journalled on said frame, gear Wheels keyed to said shaft, spaced parallel racks adapted to rest on said flat surface, said gear Wheels meshing with said racks, said frame including a first integral straight member extending at right angles to said racks, a second straight member removably aixable to said frame in spaced parallel relationship with said integral straight member, means to aiiix said second member at a pre-determined Varying distance from said first straight member, a pivot pin mounted on said frame at a point spaced from said two straight members, said pivot pin adjustably displaceable relatively to said frame for varying its distance from said first straight member, a straight arm engaging said pivot pin, a stylus carrying member slidably mounted on each of said straight members and pivotally connected to said arm at the inter-sections of the latter with said straight members, the stylus carrying member .slidably mounted on said second straight member being slidable relatively to said arm, and a tracing stylus and a marking stylus secured to said stylus carrying members.

12. A drafting instrument of the character described, comprising a U shaped frame adapted to be disposed on a nat surface, racks mounted on the parallel spaced legs of said U shaped frame, a triangular movable frame having straight base and side members, a shaft extending parallel to said base member and journalled on said frame, gear Wheels keyed to the ends of said shaft projecting from said frame and meshing with said racks, an auxiliary Wheel secured to the apex portion of said triangular frame, a plurality of spaced holes made in said side members oi said triangular frame, said holes opposed in pairs and the holes of each pair lying at an equal distance from said base member, a straight bar, pins projecting from said bar and slidably mounted thereon, said pins engageable With said holes of said side members to secure said bar l in adjustable spaced parallel relaticnship with said base member, stylus carrying members slidably mounted on said base member and on said bar, interchangeable marking and tracing styli secured tc said stylus carrying members, a pivot pin mounted at the apex portion of said triangular frame, means for displacing said pivot pin relatively to said frame for varying its distance from said base member, a straight arm pivoted at one end on said pivot pin, said arm pivotally and slidably connected to said stylus carrying members.

13. A drafting instrument as claimed in claim 12, wherein said arm projects at its other end from said base member and a circular plate 12 secured to the free end of said arm and adapted to come into frictional contact with said -at surface. i

LEON VALoIs.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 520,003 Lehner 1 May 15, 1894 1,322,592 McTaggart Nov. 25, 1919 

